1. Field of the Invention
The present invention relates to a multi-type charged particle beam exposure system which draws a pattern by a plurality of charged particle beams, an exposing method therefor, and a manufacturing method for manufacturing a device utilizing the exposing method. More particularly, the present invention relates to a charged particle beam exposure system, an exposing method therefor, and a manufacturing method for manufacturing a device utilizing the exposing method, the method permitting a proximity effect correction to be performed rapidly and appropriately, and permitting a correction, for eliminating variations among charged particle beams irradiated, to be performed at a predetermined timing, when drawing a pattern on a substrate by charged particle beams.
2. Description of the Related Art
In recent years, as means for drawing a micro-pattern on a specimen such as a semiconductor wafer or a mask substrate, an electron beam lithography system is used. In this system, however, the influence of a so-called proximity effect that causes the widening or narrowing of a pattern by backward-scattered electrons constitutes a problem.
One effective method for correcting the proximity effect is a correcting method for correcting an irradiation dose. As a method for determining the optimum irradiation dose, (a) a method using matrices (M. Parikhh, J. App. Phys. 19, p. 4371, p. 4378, p. 4383 (1979), (b) a method which uses a simple approximate solution as a formula (e.g., J. M. Parkovich, Journal of Vacuum Science and Technology B4, p. 159 (1986), or the like has been used.
The method (a) is a method wherein the relationship between the irradiation dose and the photosensitivity at each position is represented by a matrix, and the optimum irradiation dose at each position is found by obtaining the inverse matrix of the above-mentioned matrix. The advantage of this method is that the accurate optimum irradiation dose can be found if the size of a pattern, based on which the irradiation dose is set, is sufficiently reduced. On the other hand, the drawback thereof is that an enormous amount of calculation time is required. For example, in order to perform a correction with respect to all LSI chips being used directly for the drawing, it takes hundreds to thousands of hours.
The method (b) is a method wherein an approximate value Dxe2x80x2 is calculated using the following formulae (1) and (2)
Dxe2x80x2=C/(1/2+xcex7U)xe2x80x83xe2x80x83(1)
U=(1/xcfx80)∫exp{xe2x88x92(xxe2x88x92xxe2x80x2)2xe2x88x92(yxe2x88x92yxe2x80x2)2}dxxe2x80x2dyxe2x80x2xe2x80x83xe2x80x83(2)
Here, C is a constant, xcfx80 is the photosensitivity ratio of a resist of forward scattering of an electron beam and that by backward scattering. With regard to the integration range of the parameter U, the evaluation points of the irradiation dose are set to be (x, y), and the integration is performed for rectangles existing within a circle which has a center (x, y), and which has a radius two to three times larger than the backward-scattering radius, or for rectangles, some of which exist within the circle. However, even though such an approximate solution is used, it takes several hours to perform a correction with respect to all LSI chips being used directly for the drawing.
Furthermore, in a multi-type charged particle beam exposure system, which draws a pattern by a plurality of charged particle beams, it is difficult to uniformly maintain the irradiation dose of all of the charged particle beams, because of influences of heat generated by charged particle beams irradiating a substrate.
As described above, the calculation time for correcting a proximity effect requires at least several hours. On the other hand, xcfx80, a parameter for the calculation for the proximity effect correction, a backward-scattering radius, and the like, are varied depending on a resist applied to a wafer or a film material on the surface of a wafer. It is, therefore, necessary to determine the parameter (such as xcfx80 and the backward-scattering radius) for achieving the optimum proximity effect. For this purpose, the step of recalculating the correction of a proximity effect by changing the parameter, and the step of actually exposing the wafer using the recalculated proximity effect correction and then evaluating the result obtained, are performed repeatedly. This means that the electron beam lithography system is exclusively employed for tens of hours to determine the parameter. This results in a reduction in the availability of the system.
Moreover, in a multi-type charged particle beam exposure system which draws a pattern by a plurality of charged particle beams, in order to achieve an exposure with a uniform irradiation dose by eliminating variations in the irradiation dose among a plurality of charged particle beams, for example, a calibration (correction) for changing duties among the beams is indispensable.
Accordingly, it is an object of the present invention to solve the above-described problems associated with the conventional art.
In accordance with a first aspect, the present invention provides a charged particle beam exposure system which draws a pattern on an object to be exposed by a plurality of charged particle beams. This system comprises (a) a storage device storing (i) standard dose data for controlling the irradiation of charged particle beams to an object to be exposed, (ii) plural pieces of proximity effect correction data for correcting the irradiation of the charged particle beams for each incidence position with respect to the object to be exposed, in order to reduce the influence of a proximity effect, and (iii) calibration data for correcting variations in the irradiation dose among a plurality of the charged particle beams; and (b) a controller for controlling the irradiation of each of the charged particle beams, based on the standard dose data, the proximity effect correction data, and the calibration data.
The standard dose data preferably include bit map data which are determined depending on the pattern to be exposed.
Also, the standard dose data may include the data defining the bit map data and a ratio of the irradiation time with respect to the non-irradiation time.
Preferably, the present invention, in this aspect, includes means for obtaining the calibration data by measuring variations in the irradiation dose among a plurality of the charged particle beams. The above-mentioned obtaining means may include a Faraday cup.
The present invention, in this aspect, preferably includes means for selecting one piece of data suitable for the proximity effect correction with respect to the standard dose data, from plural pieces of the proximity effect correction data stored in the memory device.
In accordance with a second aspect, the present invention provides a method for correcting exposure data for drawing a pattern on an object to be exposed by a plurality of charged particle beams, comprising the step of creating standard dose data for each irradiation position of the charged particle beams in order to expose a standard pattern on the object to be exposed; the step of creating or renewing a plurality of proximity effect correction data for each irradiation position depending on conditions of the object to be exposed; the step of selecting any one piece of the proximity effect correction data, from plural pieces of the proximity effect correction data for each irradiation position; the step of performing a proximity effect correction with respect to the standard dose data based on the selected data, and exposing apattern on the object to be exposed; the step of evaluating the exposed pattern, and judging whether the selected one piece of proximity effect correction data is the optimum data for controlling the standard dose data; the step of determining the optimum proximity effect correction data for controlling the standard dose data in accordance with the judgment; the step of measuring, by a sensor, the irradiation dose of the charged particle beams from each element electron optical system, the irradiation dose having been subjected to a correction by the proximity effect correction data; and the step of determining the calibration data of each of the element electron optical systems, based on the irradiation dose measured by the above-mentioned measuring.
Whether the selected one piece of proximity effect correction data is the optimum data for controlling the standard dose data is preferably judged by comparing the exposed pattern and the standard pattern by a visual inspection.
Also, whether the selected one piece of proximity effect correction data is the optimum data for controlling the standard dose data is preferably judged by evaluating means for comparing the exposed pattern and the standard pattern.
Preferably, the proximity effect correction data is data not depending on the pattern to be exposed, but data depending on the conditions of the object to be exposed.
The conditions are preferably determined as at least one parameter among the fundamental conditions of the object to be exposed, the resist material, and a backward-scattering radius.
The above-mentioned sensor used in the measuring step may include a Faraday cup.
The present invention, in a third aspect, provides a method for manufacturing a device, comprising the step of providing an exposure system as discussed above; the step of exposing a pattern on a wafer using the exposure system; and the step of assembling the device by processing the wafer on which the pattern has been exposed.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.